Nicotine is the type of substance that is going to irritate your respiratory system. Your body sees the nicotine as a bacteria and is constantly on the defensive. This means that it is going to constantly renovate the surface epitel layers of your bronchial system. After awhile, those layers will not be able to fight as well.
How does nicotine affect the respiratory system? – http://wiki.answers.com/Q/How_does_nicotine_affect_the_respiratory_system